Christopher J A Wales

Design of a Morphing Wing tip

An initial design of a morphing wingtip for a regional jet aircraft is developed and evaluated. The adaptive wingtip concept is based upon a chiral-type internal structure, enabling controlled cant angle orientation, camber, and twist throughout the flight envelope. A baseline turbofan aircraft configuration model is used as the benchmark to assess the device. Computational fluid dynamics based aerodynamics are used to evaluate the required design configurations for the device at different points across the flight envelope in terms of lift/drag and bending moment distribution along the span, complemented by panel-method-based gust load computations. Detailed studies are performed to show how the chiral structure can facilitate the required shape changes in twist, camber, and cant. Actuator requirements and limitations are assessed, along with an evaluation of the aerodynamic gains from the inclusion of the device versus power and weight penalties. For a typical mission, it was found that savings of around...

Prescribed velocity method for simulation of aerofoil gust responses

A new method for modeling the interaction of an aerofoil with a gust using a prescribed velocity approach, called the split velocity method is presented. This approach effectively rearranges the governing equations into a form that allows for more efficient calculation and includes both the effect of the gust on the aerofoil and the effect of the aerofoil on the gust. The convection of gusts, through the domain from the far field, is investigated using the new method for a range of 1-cosine gusts. The results obtained are compared to an existing prescribed velocity approach called the field velocity method, which neglects the effect of the aerofoil on the gust. The two prescribed velocity approaches agree well for longer gusts. For shorter gusts where the gust length is close to the chord of the aerofoil, the new approach produces better results. Details of a linearized version of the split velocity method are also given. The linearized version is shown to agree well with the full method for cases when th...

Reduced order modelling for aeroelastic aerofoil response to a gust

Results for the gust response of the FFAST aerofoil calculated using computational fluid dynamics (CFD) and reduced order models (ROM) constructed using the eigenvalue realization algorithm (ERA) are presented. The CFD results are calculated using the Split Velocity Method (SVM). The SVM method rearranges the Euler equations retaining all terms after splitting the velocity into a prescribed gust and the remainder. SVM allows for the capture of the effects of the gust on the aerofoil and the aerofoil on the gust. In addition to the full SVM method a linearized version, used to generate the data for producing the ROM, is also presented. For larger gusts with over 5 ◦ changes in effective angle of attack it was found that the non-linearities due to large shock motions, which are not captured by the standard ROM, became important. So in addition a version of the ROM corrected with steady state information is presented, this gives more accurate results for longer gusts particularly when used in aeroelastic simulations.

Reduced-order modeling of gust responses

This paper describes two approaches to the construction of reduced-order models from computational fluid dynamics to predict the gust response of airfoils and wings. The first is a linear reduced-order model constructed using the eigensystem realization algorithm from pulse responses, and the second approach modifies the linear reduced-order model using steady-state data to introduce some nonlinearity into the reduced-order model. Results are presented for the Future Fast Aeroelastic Simulation Technologies wing and the Future Fast Aeroelastic Simulation Technologies crank airfoil. These show that for gusts of large amplitude in the transonic regime the response exhibits nonlinearity due to shock motion. This nonlinearity is not captured well by linear reduced-order models; however, the nonlinear reduced-order model shows better agreement with the full nonlinear simulation results.

An initial study of the flow around an aerofoil at high Reynolds numbers using continuation

Nonlinearities are an important feature of high Reynolds numbers flows about aircraft. Standard time stepping schemes, used in computational fluid dynamics simulations, are unable to capture the whole solution space, breaking down in the region of bifurcations. The extension of continuation techniques to such flows is therefore attractive. CFD schemes yield large systems of equations and the associated difficulties of applying continuation methods to such large systems need to be overcome. Whilst previous studies of fluids using continuation have been published, these are mainly limited to much lower Reynolds numbers. In high Reynolds number flows, inertial forces dominate and turbulence must be modeled. This study has shown that continuation can be used effectively for high Reynolds number flows demonstrated through the presentation of a number of test cases.

A continuation algorithm for turbulent flows around a 2D airfoil

A new code has been developed to study the parameter dependence of the nonlinear dynamics of turbulent compressible two dimensional flows. Using this code it is possible to track the change in steady state solutions, as a parameter such as angle of attack is varied, as well as changes in the stability of the solutions. Details of the development of the code and results showing both the stable and unstable steady state solutions, as the angle of attack is varied, are presented. The nonlinear nature of the Navier-Stokes equations gives rise to multiple solutions and complex dynamics as system parameters are varied. For example, hysteresis in the values of the coefficients of lift, drag and pitching moment for an airfoil with varying angle of attack is observed under certain flow conditions. To gain an overall understanding of a fluid problem, it is necessary to consider all possible solutions of the system, both stable and unstable, as the parameters on which it depends are varied. The resulting knowledge has applications in a number of areas: multivalued aerodynamic behaviour is important as the resulting widely different values of lift, and lift to drag ratio, could affect recovery from stall and/or a spin; parameter values beyond which stable steady solutions are unobtainable are important in aeroelastic calculations; attempts to produce reduced order models of complex unsteady aerodynamic stall behaviour require the dynamics of that behaviour to be first identified. There are two main numerical approaches to gaining insight into the possible solutions of a nonlinear system as the parameters on which it depends are varied. The first is to carry out time accurate simulations at a range of fixed parameters. This is the main method used in computational fluid dynamics. Such an approach is usually only able to identify stable solution branches, however Mittal and Saxena 1 conducted a numerical study using a finite element method to predict the static hysteresis around a NACA 0012 airfoil, using a incompressible solver coupled with the Baldwin-Lomax turbulence model. At higher angles of attack results were unsteady and so the time average of these was plotted as the solution. The unstable solution that separates the two branches was not calculated. The alternative approach is to discretise the problem to produce a system of nonlinear equations and then use methods from nonlinear analysis to compute solution paths. This method has the advantage that it can calculate the unstable solutions which are just as important as the stable solutions in driving the overall dynamics of the system. This latter approach has been adopted in this study and used to investigate the behaviour of the steady Navier-Stokes equations. There are several existing software packages available for carrying out the analysis of nonlinear equations, through path following, such as AUTO. However, these packages tend to be designed for low dimensional systems with dynamics dependent on multiple parameters. As a result they use direct solvers for dense matrices which make them unsuitable for analysing high dimensional systems of equations that result from the discretisation of the Navier-Stokes equations. With improvements in computational power of modern processors and increased memory capacity, with direct or iterative sparse linear solvers, it has recently become possible to extend existing nonlinear analysis methods to analyse the Navier-Stokes equations. Previous investigations into Navier-Stokes flows have mainly been on Taylor-Courette type flows 2,3 with Reynolds

Uncertainty Quantification of Aeroelastic Systems with Structural or Aerodynamic Nonlinearities

In this work, various aeroelastic approaches are used in the uncertainty quanti cation of a generic UAV wing. The di erent methods that are employed investigate varying levels of model delity, representing methods that could be used for low-order, rst-case studies, up to much higher delity methodologies. Results consider geometrically-exact structural and aerodynamic nonlinearities, and investigates the validity of using low-order simulations to predict deterministic and uncertainty bounds versus those of higher-order approaches. It is shown how correlated loads envelopes comparing strip theory aerodynamics show good agreement with higher order panel methods, even for very exible wings, but it is also seen how di erences in aerodynamic modelling (which would be equivalent in a structurally linear analysis) can e ect the results, particularly torque. It is also shown how aerodynamic delity can potentially a ect the uncertainty bounds of the computed aerodynamic loads, suggesting that low-order potential ow solvers signi cantly underestimate the uncertainty bounds compared to higher-order RANS approaches.

Active and Passive Smart Structures and Integrated Systems 2016

This work presents the lessons learned from wind tunnel tests of a droop-nose morphing wingtip as part of the EU project NOVEMOR. The design followed a sequential chain and was largely driven through optimization tools, including a glass-fiber composite skin optimization tool and a topology optimization tool for the design of internal super-elastic and aluminium compliant mechanisms. The device was tested in the low speed tunnel at the University of Bristol to determine the structural response under aerodynamic loading. Measurements of strain from strain gauges show that the structure is capable of handing the aerodynamic loads though also show an imbalance of strain between the components. Measurements of surface pressures show a small variation of cp with the 2° droop morphing variation as per the target. The wind tunnel testing showed that further developments to the design chain are necessary, in particular the need for a concurrent as opposed to sequential chain for the design of the various components. Considerations of other problem formulations, the inclusion of nonlinear finite element analysis, and ways to interpret the structural boundary of the topology optimization results with more confidence are required. The utilization of super-elastic materials in morphing structures may also prove to be highly beneficial for their performance.This work presents the lessons learned from wind tunnel tests of a droop-nose morphing wingtip as part of the EU project NOVEMOR. The design followed a sequential chain and was largely driven through optimization tools, including a glass-fiber composite skin optimization tool and a topology optimization tool for the design of internal super-elastic and aluminium compliant mechanisms. The device was tested in the low speed tunnel at the University of Bristol to determine the structural response under aerodynamic loading. Measurements of strain from strain gauges show that the structure is capable of handing the aerodynamic loads though also show an imbalance of strain between the components. Measurements of surface pressures show a small variation of cp with the 2° droop morphing variation as per the target. The wind tunnel testing showed that further developments to the design chain are necessary, in particular the need for a concurrent as opposed to sequential chain for the design of the various components. Considerations of other problem formulations, the inclusion of nonlinear finite element analysis, and ways to interpret the structural boundary of the topology optimization results with more confidence are required. The utilization of super-elastic materials in morphing structures may also prove to be highly beneficial for their performance.

Lessons learned from wind tunnel testing of a droop-nose morphing wingtip

This work presents the lessons learned from wind tunnel tests of a droop-nose morphing wingtip as part of the EU project NOVEMOR. The design followed a sequential chain and was largely driven through optimization tools, including a glass-fiber composite skin optimization tool and a topology optimization tool for the design of internal super-elastic and aluminium compliant mechanisms. The device was tested in the low speed tunnel at the University of Bristol to determine the structural response under aerodynamic loading. Measurements of strain from strain gauges show that the structure is capable of handing the aerodynamic loads though also show an imbalance of strain between the components. Measurements of surface pressures show a small variation of cp with the 2° droop morphing variation as per the target. The wind tunnel testing showed that further developments to the design chain are necessary, in particular the need for a concurrent as opposed to sequential chain for the design of the various components. Considerations of other problem formulations, the inclusion of nonlinear finite element analysis, and ways to interpret the structural boundary of the topology optimization results with more confidence are required. The utilization of super-elastic materials in morphing structures may also prove to be highly beneficial for their performance.This work presents the lessons learned from wind tunnel tests of a droop-nose morphing wingtip as part of the EU project NOVEMOR. The design followed a sequential chain and was largely driven through optimization tools, including a glass-fiber composite skin optimization tool and a topology optimization tool for the design of internal super-elastic and aluminium compliant mechanisms. The device was tested in the low speed tunnel at the University of Bristol to determine the structural response under aerodynamic loading. Measurements of strain from strain gauges show that the structure is capable of handing the aerodynamic loads though also show an imbalance of strain between the components. Measurements of surface pressures show a small variation of cp with the 2° droop morphing variation as per the target. The wind tunnel testing showed that further developments to the design chain are necessary, in particular the need for a concurrent as opposed to sequential chain for the design of the various components. Considerations of other problem formulations, the inclusion of nonlinear finite element analysis, and ways to interpret the structural boundary of the topology optimization results with more confidence are required. The utilization of super-elastic materials in morphing structures may also prove to be highly beneficial for their performance.

Chiral Morphing Wing Tip Design and Test

This work presents a proof of concept morphing design to control twist of a wing tip. The morphing is achieved by exploiting the properties of a chiral structure to undergo large shape changes with small local strains. Details of the approach for designing a wind tunnel model containing a chiral internal structure are discussed, along with an evaluation of the actuator requirements. The static performance of a demonstrator chiral wing tip is also compared to numerical predictions.